A fuse is an electrical connection in the form of a fusible link. Fuses have many applications in semiconductor industry. In one common application, a serial number or identification number is placed on a chip by setting fuses. In a second common application, a block or array of dynamic random access memory (DRAM) devices may be repaired by substituting a redundant block (array) for a failed block or array that could otherwise render the entire device inoperative. By selectively blowing fuses to select the DRAM device block (or array), the failed block is deactivated and the substituting redundant block is activated. The same method is used for static random access memory (SRAM) blocks. By replacing defective blocks (arrays) with redundant blocks, integrated circuit DRAM or SRAM yields are significantly improved.
In the past, a laser beam had been used to blow selected fuses in the DRAM or SRAM device repairing process described above. The laser blowing technique, however, has become increasingly difficult as the size of semiconductor devices decreases. As semiconductor devices become smaller, fuses in these devices have shrunk in size such that the fuse pitch is now smaller than the diameter of conventional laser beams. In addition, the density of circuits of semiconductor devices has increased. It is more and more difficult to blow a fuse with a laser beam without inadvertently damaging another part of the same fuse or neighboring circuits on the same semiconductor device. Furthermore, repairing or programming a semiconductor device requires blowing open thousands of fuses. It is also time consuming to blow open these many fuses by a laser beam.
More recently, electrical-fuses (e-fuses) have been developed for the DRAM or SRAM device repairing process. E-fuses can be blown by passing a high density electrical current through the fuse element. E-fuses take advantage of the electro-migration effect to selectively open up metal connections at desired locations within the fuse. The electro-migration effect has long been identified as a major metal failure mechanism. Electro-migration is a process in which ions of a metal conductor move in response to a high density current flow through the metal conductor. The ion movement leads to the formation of voids in the metal conductor. An e-fuse typically has a two-dimensional dog-bone shape with a narrow neck portion between two larger contact regions. Because the void formation rate is a function of current density, the narrow neck portion with the smallest cross-sectional area will experience the highest current density of the fuse and become discontinuous.
However, the conventional two-dimensional e-fuse generational scaling poses a barrier for on chip autonomic programming. As the operating voltage of semiconductor devices continues to be scaled down, it is increasingly difficult to achieve sufficiently high programming current to blow e-fuses in the devices. In addition, the high current needed to program the conventional e-fuse requires a wide programming transistor which consumes a significant silicon area. Accordingly, there exists a need for an e-fuse in which the absolute programming power can be scaled with the existing supplies.